The present invention relates to a reflective article, in particular for the rear-view mirrors for motor vehicles, having hydrophilic properties and an attenuated reflection factor. The present invention also relates to a process for the production of such an article.
Mirrors comprising a metal layer (generally made of silver, aluminum or chromium) applied either to the rear face of a transparent substrate, i.e. on the face remote from the observer, or on the front face of the substrate, thus the face directed towards the observer, are known. With a metal layer of chromium having a thickness in the order of 40 to 60 nm, a light reflection of about 65% is obtained, which is perfectly satisfactory for use as a rear-view mirror. However, with more significant light reflections the rear-view mirror has the disadvantage of causing glare for the driver.
Mirrors with a surface, which has been rendered hydrophilic, are also known (see EP 689 962, EP 1 022 588 or JP 2001033607, for example).
The hydrophilic character of a surface increases its surface energy, which allows drops of water to spread in a film instead of forming droplets. On a non-hydrophilic mirror the rain forms droplets, which obstruct visibility. On a mirror with a hydrophilic surface, the water spreads to form a film to allow better visibility. Various materials are known for their inherent hydrophilic properties, in particular titanium oxide and silicon oxide.
In addition to its hydrophilic properties, titanium oxide, particularly when crystallised in the form of anatase, is also well known for its inherent photocatalytic properties, i.e. it is able to degrade organic matter when stimulated by light or UV irradiation.
Patent applications EP 978 494 and EP 1 099 671 describe anti-fog mirrors comprising a reflective metal film respectively on the rear and front face and a TiO2/SiO2 coating stack on the front face.
Since the TiO2 layer has a high refractive index (n=2.4), the reflection factor of the coating stack in the visible range is elevated, in the order to 80% for a stack of neutral colouration. To reduce glare, the thicknesses of the layers must be selected so that the wavelength of the reflected light has a peak between 400 and 510 nm, which gives a reflected blue colour and a light reflection in the order of 60%. EP 1 099 671 provides that a reflection-adjusting layer can be added between the reflective film and the TiO2 layer to prevent excessive reduction of the light reflection.
Coating stacks with alternating layers of high and low refractive index are commonly used to increase the light reflection. Documents EP 456 488 and EP 1 040 963 describe mirrors with high light reflection (>70%) using a metal layer as reflective layer, and a succession of low index layers (SiO2) and high index layers (TiO2) to increase reflection.